Polybutene is generally produced by polymerizing C4 olefin including isobutene in the presence of Friedel-Craft type catalyst, and has about 300˜5000 of number average molecular weight (Mn). Remains after extracting 1,3-butadiene from C4 olefin is called as C4 raffinate-1, and the C4 raffinate-1 comprises paraffin such as iso-butane and normal-butane, and olefin such as 1-butene, 2-butene, and isobutene. The isobutene content in the C4 raffinate-1 is generally about 30˜50 weight %. The C4 raffinate-1 is generally used for producing methyl-t-butylether (MTBE) which is useful as an octane number improver, or polybutene. The produced polybutene is mainly composed of isobutene units since the isobutene has the highest an octane number improver, or polybutene. The produced polybutene is mainly composed of isobutene units since the isobutene has the highest reactivity among the olefins in the C4 raffinate-1. Polybutene can also be produced from butane-butene oil (B—B oil) which is a C4 mixture derived from crude oil refining process. Alternatively, polybutene can be produced from pure isobutene.
The viscosity of polybutene increases as its molecular weight increases and the viscosity is about 4˜40000 cSt (centi-stocks) at 100° C. Polybutene is pyrolyzed at the temperature of more than 275° C. without leaving residue, and has high solubility in lubricant or fuel because of its branched alkyl structure. For these reasons, polybutene is used as an anti-scuff agent or a viscosity index improver in engine oil, or used as detergent by being mixed with fuel of internal-combustion engine of a vehicle. In the past, the high reactive polybutene is not preferred since the same is mainly used for adhesive or insulating oil. However, the demand for high reactive polybutene constantly increases. This is due to the fact that the use of high reactive polybutene having a polar group as fuel detergent or lubricant additive gradually increases.
The most widely used polybutene formed by introducing a polar group is polyisobutenyl succinic anhydride (PIBSA) manufactured by reacting polybutene with maleic anhydride. Most of lubricant additive or fuel detergent is produced with PIBSA as an intermediate. In case that the double bond of polybutene is positioned at its end, PIBSA can be obtained in high yield. However, when the double bond is positioned in the interior of the polybutene and the number of alkyl group substituted to the double bond increases, reactivity of polybutene is lowered, which decreases the PIBSA yield. For increasing the reactivity of polybutene, a method of chlorinating polybutene with chlorine gas and then, reacting the chlorine product with maleic anhydride is known. However, this method is not preferable in an economic and/or an environmental aspect since it costs much due to the expensive equipment for preventing corrosion of a reactor, and a large quantity of basic solution should be used to neutralize the un-reacted chlorine gas. In addition, when PIBSA containing a large amount of chlorine is used for fuel additives, it may cause a corrosion of engine. Accordingly, researches for increasing the reactivity of polybutene by changing its polymerization condition are constantly in progress. Types of double bond that effect the reactivity of polybutene depend on the number of alkyl group substituted to the double bond as shown in equation 1.

As Friedel-Craft type catalyst for producing polybutene, aluminum trichloride or boron trifluoride are generally used. The high reactive polybutene that contains relatively large amount of terminal double bond is obtained when boron trifluoride is used. For example, it is reported in Journal of Polymer Science, Symposium no. 56, 191-202(1976), that content of terminal double bond increases up to 40% for 5˜7 minutes of contact time when boron trifluoride or complex compound of boron trifluoride are used with co-catalyst such as acetic acid or water. According to this method, polybutene which contains high content of terminal double bond can be obtained, while the content of terminal double bond is 5˜20% when conventional aluminum trichloride is used. However, there is also disclosed that as the contact time is longer, the position of the vinylidene (terminal double bond) of the produced polymer moves to the internal position of the polymer, and therefore, the reactivity of polybutene decreases. This is indirectly shown in Khim I Teknol, Topliv 1 masel, vol. 10, pp 23-26, written by Mullin M. A. According to this literature, methanol or mixture of methanol/ethanol and complex compound of BF3 are used, and the contact time is 30˜40 seconds. This means that the catalyst should be very carefully used in the polymerization. The fact that the contact time should be maintained to be short when boron trifluoride catalyst is used for the isobutene polymerization is also emphasized in European Patent No. 016312 A1. There is disclosed that the contact time and the concentration of catalyst should be strictly controlled, and especially, the contact time should be maintained within 40 seconds to prevent the double bond isomerization.
European Patent No. 400,905 A1 discloses that when boron trifluoride-ethanol complex is used, the contact time can be prolonged to more than 1 minutes, possibly 8˜70 minutes, and more preferably 12˜20 minutes without inducing the isomerization of double bond in the product, and therefore, reaction variables can be effectively controlled. European Patent No. 400,905 A1 is regarded as an advanced one because the product can maintain the content of terminal vinylidene of more than 70% while maintaining the contact time of more than 8 minutes.
U.S. Pat. No. 5,688,887 discloses a method for producing polybutene having more than 80% of terminal vinylidene content by using boron trifluoride-ether complex catalyst, wherein the ether have at least one tertiary alkyl group. In this method, less isomerization is induced even though the contact time is prolonged. The reason of the less isomerization under the prolonged contact time is that the catalyst does not induce an initiation reaction of the isomerization. That is, the catalyst does not produce proton, and thus prevents that proton decreases the content of the terminal vinylidene by isomerization. According to the examples of the above-mentioned patent, the most desirable result is obtained when ether having both a secondary alkyl group and a tertiary alkyl group (for example, isopropyl t-butylether) is used. However, the above-mentioned ether compound is not a commercialized material. Therefore, to use the material as the co-catalyst (initiator), an additional equipment to produce the compound is required. For this reason, the above-mentioned method is not commercially implemented.
U.S. Pat. No. 5,408,018 discloses a method for producing polybutene containing more than 80% of terminal vinylidene content and having a narrow molecular weight distribution by using secondary alcohol-boron trifluoride complex as a catalyst system. However, this method has disadvantages in that the reaction condition, for example, reaction temperature, is difficult to control since the reaction temperature is relatively low, and the contact time should be controlled within 9 minutes.